The invention relates to a process for the thermal conversion of a charge consisting of a heavy fraction of organic material in the presence of oxygenated organic compounds of sulfur or of nitrogen, and to a composition comprising these compounds.
It is particularly applicable in the industry for the refining of petroleum and coal and particularly for processes of viscoreduction and catalytic hydroprocessing.
Improvement in the thermal treatment processes used in the petroleum industry for the refining of fossil organic materials rich in heavy polyaromatic structures, coke promoters, such as heavy petroleums and related materials: bituminous schists, coal, asphaltic sands and refining residues, involves the control of the processes of radical transformations by the employment of solvents or effective additives.
Numerous works have been devoted to the employment of hydrogen donor solvents (hydroaromatic structures such as tetraline, dihydroanthracene or partially hydrogenated petroleum fractions), capable of efficiently inhibiting the development of the radical reactions of chain polycondensation or chain polymerization.
However, under identical conditions, the use of an efficient hydrogen donor results in a conversion of light fractions which is more moderate when there are eliminated from the reaction medium reactive intermediates which promote processes of fragmentation of the chains. This aspect of the problem has led to the association of additives capable of performing as a group radical capture and activation of the fragmentation of the polymolecular agregates present in these heavy fractions.
Various studies mention the effect of hydrogen sulfide present during treatment of petroleum fractions rich in sulfur as a compound capable of a double catalytic role; on the one hand, the improvement of the kinetics of hydrogen transfer and hence of the efficiency of free radical capture on the other hand, activation of fragmentation reactions. However, their synergetic use with hydrogen donor solvents has been only a little exploited.
Recent works describe the activating effect of certain thiols (EP 175,511) and organic disulfides (benzenethiol, dodecanethiol and the like, and diphenyldisulfide-) as well as a precursor of hydrogen sulphide ammonium sulphide. These compounds have the drawback of being expensive and of partly decomposing during the thermal treatment; they then can not be regenerated. In a prior document, in particular, dimethyldisulfide is used as promotor of the viscoreduction in the presence of nickel naphthenate (BE 901,092).
Other types of activators have been recommended in the prior art, such as radical generators (US 4,298,455); generally, these additives have various reactional insufficiencies, particularly:
the thermal formation field of the reactive species is too limited from generators such as hydrogen peroxide, hydroperoxides and organic peroxides. This temperature, generally less than 200.degree. C., leads to insufficient stability for their effective action in the medium at the temperatures usually utilized.
their action consists rather of a prior chemical modification to the thermal treatment proper; in addition poor selectivity is observed due to the fact of the often sudden and exothermic decomposition of these compounds;
they show a potential non-regenerability due to the fact of their total decomposition.
In addition, the prior art describes in patent EP 183,269 a mixture of compounds based on molybdenum selected from anong the mixture of molybdenum dithiophosphate and carboxylate and the mixture of molybdenum dithiocarbonate and carboxylate.
Finally, the U.S. Pat. No. 4,298,455 mentions the association of azobisisobutyronitrile with sulfurized or chlorinated compounds.
It is a particular object of the invention to remedy the above-indicated drawbacks.